WO2007006375A1

WO2007006375A1 - Hf-filter with improved adjacent channel suppression

Info

Publication number: WO2007006375A1
Application number: PCT/EP2006/005270
Authority: WO
Inventors: Thomas Bauer; Christian Math
Original assignee: Epcos Ag
Priority date: 2005-07-08
Filing date: 2006-06-02
Publication date: 2007-01-18
Also published as: KR101270078B1; DE102005032058B4; DE102005032058A1; KR20080028465A; JP5108758B2; US8179211B2; US20100127799A1; JP2009500928A

Abstract

The invention relates to a filter with a first partial filter (TF1), comprising a series resonator (S1) and at least two parallel resonators (P1, P2) that are arranged in respective parallel branches, and with a second partial filter (TF2) configured as a DMS filter. The filter also comprises a housing with a plurality of internal housing contacts (GKi) on a base plate that are connected to terminal areas on the substrate (SU) and external housing contacts (GKa), fewer than the internal contacts, that are connected to the internal housing contacts (GKi) via lines (DL1, DL2) guided within the base plate. At least two lines for connections to ground of the first parallel resonator (P1) and the second partial filter (TF2) are guided separately in or on the base plate and are connected to at least two different external housing contacts (E4, E2).

Description

description

HF filter with improved backbone suppression

RF filters are needed especially in mobile communication terminals. Most of them are designed for use in mobile radio systems that transmit and receive in different but closely spaced frequency bands. The receive filters are usually designed as a bandpass whose passband corresponds at least to the bandwidth of the RX band. It is usually necessary that the frequencies of the associated TX band are suppressed.

Different technologies are suitable for the production of HF filters. Dielectric filters are made from discrete L and C elements and require a variety of discrete elements to provide the required filter characteristics. Microwave ceramic filters are inexpensive to produce, have a low insertion loss and are usually too large for installation in miniaturized terminals. Good electrical properties are offered by filters based on bulk wave resonators or surface acoustic wave devices. Particularly preferred are SAW or surface acoustic wave devices which are characterized by a small size and a large variety with respect to the electrical parameters to be set

SAW-based RF filters may be constructed as a DMS (dual-mode SAW) filter or as a reactance filter of a plurality of resonators interconnected in a serial and parallel branches in the form of a ladder-type arrangement or a lattice arrangement , In addition to the small size and the ease of manufacture, a given bandwidth is required for an HF filter, wherein the pass band should fall to the stop band with a steep slope. The insertion loss in the passband should be minimal in order to minimize the energy losses. On the other hand, an RF filter should be power-compatible and, even with high input or output power, should not permanently damage the electrode structures.

To improve the Gegenbandunterdrückung, in an RX filter, for example, to suppress the TX frequencies has already been proposed to connect a two-track three-converter DMS filter at the input and output with parallel resonators. However, such a structure proves to be not sufficiently powerful and has a relatively large insertion loss.

A pure reactance filter requires too large a number of base elements to achieve sufficient backbone rejection, with each fundamental element being composed of a series resonator and a parallel resonator. However, as the number of basic elements increases, the insertion loss of such filters deteriorates.

It is therefore an object of the present invention to specify an HF filter which has good counterband suppression and combines these with other advantageous properties.

This object is achieved by an RF filter having the features of claim 1. Advantageous embodiments of the invention can be found in further claims. It is proposed an RF filter, which is composed of a first and a second sub-filter. The first sub-filter is designed as a reactance filter and has at least two parallel resonators and a series resonator. The second sub-filter is designed as a DMS filter and has at least three interdigital transducers. To achieve sufficient backbone suppression, this filter is incorporated into a specially designed housing in which the ground terminals of the first parallel resonator and the second sub-filter are routed separately and fed to separate outer housing contacts.

It turns out that with these separate ground lines, the galvanic coupling between the different filter elements is reduced, which otherwise leads to unwanted signals at the output. Depending on their nature, these unwanted signals can impair the passband, lead to unwanted peaks in the stopband or generally distort the useful signal with signals to be suppressed.

First and second sub-filter can be constructed on a common piezoelectric substrate and interconnected there. The first sub-filter is preferably connected to the input. This has the advantage that the more powerful reactance filter as the first sub-filter absorbs part of the power of the received signal, so that the second sub-filter, so the DMS filter is loaded with a lower signal level. Especially in the opposite band, the reactance filter absorbs most of the power. This makes the proposed RF filter more power-efficient overall. With the proposed filter, a good Gegenband- suppression and a high edge steepness is achieved. Here, the good Nahbereichsunterdrückung a reactance filter is used, which can be well adjusted by suitable frequency position of the poles, in particular by a suitable choice of the resonant frequency of the parallel resonators. Good far-range rejection, on the other hand, is provided by the DMS filter. In combination of the two sub-filters, the advantageous properties of the different filter types are added in the combined RF filter.

The housing of the filter may include a base plate having at least one dielectric layer that is substantially electrically nonconductive. In the case of a plurality of dielectric layers, a metallization plane can be arranged in each case between two layers. In the metallization level printed conductors or in general an interconnection are structured. Through vias through the dielectric layers, the tracks and circuit elements of the at least one metallization level are connected to inner and outer housing contacts. By plated-through is understood to be a hole leading through one or more dielectric layers and filled with a conductive material or at least conductive coated.

The inner housing contacts serve to connect the substrate contacts of the first and second sub-filters, while the outer housing contacts serve to connect the filter to an external circuit environment. Preferably, the ground terminal of the first parallel resonator closest to the filter input is separately and separately routed from other lines through the housing and in particular through the base plate and directly to a first one connected external housing contact. This ensures that galvanic coupling effects with the first parallel branch are only caused by possible impedances in the external circuit environment. Usually, however, the external ground contacts are very well connected to the ground of the circuit environment, so that galvanic coupling effects in the form of electrical crosstalk are minimized.

The connection between the ground terminal of the first parallel resonator and the first outer housing contact is rectilinear and formed exclusively as a via. This ensures that for a given thickness of the housing or the base plate of the housing, the inductance associated with this line is minimized. As a result, an increase in the PoI zero pitch of the resonator is avoided and a greater steepness of the left flank can be achieved. The attenuation at very high frequencies is thereby improved. This with respect to the galvanic coupling optimized line through the base plate is particularly advantageous for the first parallel branch, since its high power consumption and thus high current flow, due to the location at the filter inlet and a high potential for Having couplings with other lines and metallizations.

It is also advantageous to lead the ground terminal of the second parallel resonator separated from other feedthroughs through the housing and to connect it to an outer housing contact, for example the housing contact of the first parallel resonator. Thus, a connection of the two ground terminals of the first and second parallel resonator only at the level of the outer housing contact, which is usually a good mass, or with a Good ground is connected, so that only for this reason, the galvanic coupling between the two ground lines is minimized.

To further improve the Gegenbandunterdrückung a second series resonator and in a third parallel branch, a third parallel resonator can be provided. The ground terminal of the third parallel resonator is preferably connected to a second outer housing contact, which is not identical to the first housing contact.

Thus, the coupling of the first and third parallel branch or of their ground connections is reduced.

A suitable filter function is achieved when the second sub-filter has a DMS track with five transducers. Alternatively, it is also possible to carry out the second sub-filter with two DMS tracks connected in parallel with three transducers each. This further improves the loss characteristics compared to a single-track three-transducer DMS arrangement.

To improve the performance of the reactance filter, it is proposed to cascade at least the first series resonator, preferably also the first parallel resonator and optionally further series resonators, that is to split into two series-connected partial resonators. In turn, in order to maintain the impedance of a cascaded resonator, the resonator area must be increased, which for the entire resonator, for example in a two-cascade, means a quadrupling of the resonator area compared to an unsplit resonator. This can be achieved by increasing the number of fingers and / or increasing the aperture become. Together with the now low voltage applied to each of the series-connected sub-resonators, this results in a significant improvement in the power compatibility of the cascaded resonator.

The RF filter may have an unbalanced input and an unbalanced output. In this case, it is sufficient if the housing has four outer housing contacts. If, however, the output is switched symmetrically, then a further housing contact is required, so that at least five outer housing contacts must be present. However, it is always possible to provide a larger number of outer housing contacts, which are generally disadvantageous in terms of their space requirements and the increased circuit complexity when connecting the filter to an external circuit environment. However, without much extra effort, an odd number of external case contacts can be increased by one to the next even number.

In order to avoid damage to the filter due to a flashover of electric charges resulting from the pyroelectric effect, it makes sense to connect the masses separated on the base plate to the substrate with high resistance (for example with at least one kilo ohm). This can be realized for example by metallic meander-shaped structures on the substrate surface. Such a high-impedance connection does not affect the crosstalk and thus the counterband suppression.

An improved edge steepness can be achieved if in the second sub-filter, the adjacent terminal electrode fingers of different transducers are both hot or both cold connected. This means that the both adjacent electrode fingers of different transducers are to be connected to either a signal line or both to a ground terminal.

A shielded and leaktight improved housing is obtained when the substrate with the subfilters in the housing is placed between the baseplate and a lid in which the lid comprises at least one electrically conductive layer. To improve the shield, the cover is electrically conductively connected to the ground connection within the base plate and further connected to a ground terminal of the filter or to a connected to ground outer housing contact of the RF filter. The electrically conductive cover of the housing can be connected via several points to the ground connection within or on the base plate. Thus, different ground terminals of the filter can be connected to each other via the cover, which are separated in the base plate or on the substrate. Preferably, the lid is connected unbalanced to the interconnection. Advantageously, an input side improved ground connection of the lid, which is made over more parallel and switched vias as the output side.

Usually, the number of ground terminals present on the substrate for the two sub-filters exceeds the number of outer housing contacts. It is therefore proposed to provide inside the housing and in particular inside the base plate at least two electrically mutually insulated inner ground surfaces, each connecting a plurality of ground terminals of the first and second sub-filter with each other. The inner ground surfaces are in turn connected to the outer housing contacts via through-connections. In this case, it is possible to use a plurality of plated-through holes for connecting the inner ground areas to the outer housing contacts, as a result of which the inductance lying in the common ground branch is reduced. This reduces the galvanic coupling of the mass branches connected in this way and thus improves the selection behavior of the filter.

A further improvement of the passband and in particular a steeper left flank can be obtained if capacitors are connected in parallel to the parallel resonators. Such parallel capacitances are known to reduce the pole-zero spacing of the resonators and thus to improve the edge steepness. These can be advantageously realized in the form of metallic structures on the substrate surface. It is possible, for example, to design the capacities as interdigital structures. In order to achieve that these interdigital structures act as pure capacitance as possible and produce no losses in the form of radiated waves, it is advantageous to select a finger period for them which is significantly smaller than the finger period of the transducers of the first and second sub-filters.

Another possibility for preventing the emission of acoustic waves from the capacities realized as an interdigital structure consists of rotating the interdigital structure and aligning it along a crystal axis of the substrate in which no waves are excited. If, for example, a substrate made of lithium tantalate (LT) is used, this can be achieved with a rotation of 90 degrees. However, the capacities can also be realized by using differently designed metallic structures. In the following, the proposed RF filter will be explained in more detail on the basis of exemplary embodiments and the associated figures. These are purely schematic and therefore not true to scale.

Show it:

FIG. 1 shows a first possible electrode structure for first and second sub-filters,

FIG. 2 shows three metallization levels of a two-layer base plate,

FIG. 3 shows different schematic cross sections through housings with one-layer and two-layer base plates,

FIG. 4 shows an equivalent circuit diagram of a possible interconnection of the filter elements,

FIG. 5 shows a second electrode structure for first and second sub-filters,

FIG. 6 different possibilities for the realization of parallel capacities,

FIG. 7 shows the transmission curve of a filter according to the invention in comparison with the prior art,

FIGS. 8 and 9 compare the transfer curve of proposed filters with test structures in which inner masses in the housing are connected to one another, FIG. 10 shows the effect of a symmetrical connection of the housing cover in comparison to an asymmetrical connection,

Figure 11 shows two ways to split a resonator in two sub-resonators.

Advantageous topologies for the first sub-filter consist of three to five basic elements, which can be realized in a resonator sequence PSPSP or PSPSPS viewed from the filter input, where P stands for a parallel resonator and S stands for a series resonator. Figure 1 shows the metallization structure on the piezoelectric substrate for the first and second sub-filters, wherein for the first sub-filter six resonators S, P are used, which are connected in the order PSPSPS and form five basic elements. The first parallel resonator Pl is arranged in a first parallel branch, which is connected directly to the input IN. Also directly connected to the input IN is the first series resonator Sl. Between each two series resonators, a parallel branch is arranged with a parallel resonator. The third series resonator S3, which terminates in the first sub-filter, is connected to the input of the second sub-filter.

The second sub-filter TF2 consists of five interdigital transducers, wherein three transducers are connected to the input side or to the output of the first sub-filter and two transducers to the output OUT. Transducers connected to the input and output are arranged alternately. The finger arrangement of the individual transducers is designed in the second sub-filter TF2 in single-ended operation, that is to say in the case of unbalanced operation on both sides, such that a terminal electric motor the fingers of an input transducer and the directly adjacent terminal electrode fingers of an output transducer are here each at a hot potential. Each transducer consists of two intermeshing comb-like electrode structures, also called interdigital structure. In each case several of electrode fingers are connected to a common busbar. While the signal is applied to one busbar, the other busbar of the same converter is in each case connected to a ground connection MA. In the second sub-filter TF2, the three input transducers are connected in parallel and connected with their hot busbars to the output of the third series resonator. Likewise, the two hot busbars of the two output converters connected in parallel are connected to the output OUT. The illustrated filter is therefore asymmetrically operated on both sides, so that on the input and output side only one signal-carrying line is needed. Basically, as with practically all HF filters, it is possible to swap input and output of the filter.

At further terminals, the first sub-filter TFl has a ground connection for each of the three parallel resonators, while the second sub-filter TF2 has a ground connection for each of the five transducers. This means a total of eight ground connections, an input and an output, which are formed on the surface of the substrate as connection pads or as solderable metallized surfaces.

FIG. 2 shows, in a schematic embodiment, a possible embodiment of an interconnection to be implemented within the housing on the basis of three metallization levels. Figure 2a shows the surface of the base plate GP of the housing corresponding to one of the number of terminals of the filter Number of inner housing contacts GK ₁ has. Based on the embodiment shown in Figure 1, this would be ten contacts. In the selected exemplary embodiment, however, the three ground connections MA shown below in FIG. 1 are already connected to one another on the substrate. For this purpose, the two connections connected to the output transducers are led separately to the inner housing contacts GKi, so that nine inner housing contacts are required for connecting the connections on the substrate. FIG. 2a shows a tenth connection, which is introduced solely for reasons of symmetry and serves for the stability of the housing. Furthermore, cover contact connection surfaces DK are arranged on the surface of the base plate shown in FIG. 2a and are electrically connected both to the housing cover and to the ground connections in the interior of the baseplate. Accordingly, these cover contact terminal areas are arranged outside the area provided for the substrate SU, which is identified by a dashed line in FIG. 2a.

FIG. 2b shows the metallization of the central metallization plane, which is separated from the metallization plane illustrated in FIG. 2c by a dielectric layer DL1 from that shown in FIG. 2a and by a further dielectric layer DL2. The dielectric layers are preferably made of ceramic, but may be made of other materials and in particular plastic material or glass. In the middle metallization plane according to FIG. 2b, two ground surfaces C2 and C4 are provided. The plated-through holes to the upper metallization level are marked by crosses. Accordingly, it follows that the ground plane C2 has five inner housing contacts of the upper metallization level and, accordingly, five ground terminals of the filter connected is. Furthermore, the inner ground surface C2 is connected to a cap contact terminal L3 on the first metallization level. The second ground plane C4 is connected to only one inner housing contact (G2) for a ground connection and to two cover contact terminals L1, L2. A conductor track structure C3 represents an electrical connection between the two terminals of the output transducers of the second sub-filter TF2. A further insulated track conductor C1 is connected to the internal housing contact II provided for the input IN. Another contact C5 of the middle metallization level is connected to an inner housing contact provided for a ground connection G1.

Figure 2c shows the lower metallization, which is formed by four outer housing contacts GK _a . The through contacts to the middle metallization level are again marked by crosses. It follows that the first outer housing contact El via a via with the conductor track Cl and this is connected via a via with the input of the first sub-filter. A third external housing contact E3 is connected via a through-connection with the conductor track C3 and this in turn is connected to the two terminals of the two output transducers of the second sub-filter. The inner ground surface C2 is connected via three plated-through holes with the second outer housing contact E2. The fourth outer housing contact E4 is connected via two vias to the inner ground plane C4 and via a via to the terminal C5 on the central metallization level.

FIG. 3A shows a cross section along the section line AA 'indicated in FIG. 2 through the base plate, substrate and cover of the housing. From the figure shows that the Substrate SU is connected here via bumps BU designed as solder joints with the inner housing contacts on the surface of the base GP. Also on the base GP sits on the housing cover D, which covers the substrate SU below. For example, the housing cover D is formed as a metallized film which is laminated on the substrate on the surface of the base plate GP. However, the lid D can also be rigid and placed on the base plate. It is also possible to close the gap between the substrate SU and the surface of the base plate GP at the edge of the substrate and to produce the lid by direct metallization of the surfaces.

According to the metallization pattern illustrated in FIG. 2, the baseplate GP here comprises a first and second dielectric layer DL1, DL2 having a first metallization level on the surface of the baseplate, a second metallization level between first and second dielectric layer, and a third metallization level on the underside. The electrical connections between the metallization levels are made via vias made, for example, as metallized holes through the dielectric layers. The metallization within the via can close the holes or even cover only the edges of the corresponding holes.

The metallizations of the metallization levels are, for example, printed or produced in a thin or thick-film process.

It is also possible to carry out the metallizations by a combination of thin and thick film techniques. For example, a base metallization can be applied structured and galvanically reinforced.

FIG. 3A also shows that the inner housing contact G1, which is connected to the ground terminal of the first parallel resonator P1, is connected directly to the outer housing contact E4 through two plated-through holes arranged through the two ceramic layers. The inner housing contacts G2 and J1, which are connected to metallizations C4 and Cl in the second metallization, are only offset in the plane with corresponding outer housing contacts. The metallized cover is connected to a cover contact connection surface L2 via a through-connection with the metallization surface C4 of the middle metallization level and via another through-connection to the outer housing contact E4.

FIG. 3B shows a schematic cross-section of a filter in which the substrate SU is glued into a housing consisting of a base plate GP and a lid D and contacted with bonding wire connections. The through contacts to the outer housing contacts are not shown in the figure.

FIG. 3C shows, in a schematic cross section, a filter in which a lower housing part is formed from a single-layer base plate GP and a frame on which the substrate SU is seated as a cover. The connections of the substrate SU to the inner housing contacts are e.g. via metallic structures, in particular via bumps possible.

FIG. 4 shows a schematic equivalent circuit diagram of the filter including the connections provided in the base plate and their parasitic inductances (feedthrough inductances). In the figure, the various filter elements are separated according to the place or their origin. Differences are therefore from top to bottom, the level of the filter structures on the substrate, the level of the inner housing contacts, the plane of the first dielectric layer DL1, which manifests itself only in the form of Durchführungsinduktivitäten, the central metallization MM, the second dielectric layer DL2 with their bushing inductances and finally the level of the outer housing contacts GK _a . The inductances on the substrate are neglected. The inner housing contacts GK ₁ are found in the uppermost metallization level, the contact Il being connected to the input, Gl to the first parallel resonator P1, G2 to the second parallel resonator P2, G3 to the third parallel resonator P3. The ground contacts of the second sub-filter TF2 on the side of the output terminals are already connected to one another at the level of the substrate metallization SM and to a single inner housing contact G7. With the housing contacts G4 and G5, the other two ground terminals of the second sub-filter are connected. The two outputs are connected to housing contacts Ol and 02.

From the figure can be clearly seen that the ground terminals of the first two parallel resonators Pl and P2 are separated from each other by the base plate of the housing and connected only at the lowest Metallisierungsebene with the outer housing contact E4. As a result, the two parallel resonators are well decoupled from each other. The two outputs of the second sub-filter are guided separately from one another to the central metallization level MM and are only connected there via the metallization C3. The ground connections of the third parallel resonator as well as all ground Terminals of the second sub-filter are connected to the metallization surface C2 on the middle metallization level MM and connected from there via three parallel vias to the outer housing contact E2, which represents a ground connection.

The ground connection scheme shown in FIG. 4 is optimized for the exemplary embodiment selected and illustrated in FIG. 1 and exhibits optimum properties with regard to selection and counterband suppression. If more outer housing contacts are available, it is possible to additionally separate the ground connections for the first and second parallel resonator and to supply them to separate outer housing contacts. In the next step, the ground contact for the third parallel resonator could still be fed its own external housing contact. Separation of the ground connections of the second sub-filter with respect to the input and output transducers would further improve selection and counterband suppression.

The housing or the base plate realized here as a multi-layer structure is optimized in such a way that the feedthrough inductances are minimal. This is achieved in particular with short vias or with a small thickness of the dielectric layers, but also via parallel feedthroughs. Furthermore, the inductance can still be influenced by the geometric configuration of the via. With low inductance values of the plated-through holes, a passband with steep flanks is achieved. If a plurality of ground connections are combined on the middle metallization level MM and supplied to an outer housing contact by means of a single plated through-hole, for example the through-contact tion, which connects the inner metal surface C2 with the housing contact E2, so this last common via is particularly critical with respect to their inductance value and affects the coupling of the ground connections particularly strong. It may therefore be useful to make the second dielectric layer thinner than the first dielectric layer.

In a variation of the exemplary filter shown in Figure 4, it is possible to already connect the ground terminals connected to the inner housing contacts G3 and G7 to one another on the substrate, resulting in even a slightly higher selection. Not shown in the figure 4 is the connection of the housing cover D, via which the ground surfaces C2 and C4 are indirectly connected. Because both C2 and C4 are directly connected to the good masses E2 and E4, the influence of the lid is minimized but still distinct, as shown later in FIG. 10.

Also not shown in the equivalent circuit diagram are high-impedance connections, with which the housing contacts G1, G2, G7 and G3 or the connections connected to them are connected to one another on the substrate in order to dissipate charges arising from the pyroelectric behavior of the substrate harmlessly for the component. These can occur in particular in the case of temperature changes and, in the event of flashovers, damage or even destroy the metallization structure or the substrate.

In Figure 5, the metallization scheme shown in Figure 1 for the two sub-filters is varied to the effect that now a symmetrical operation is made possible at the output. For this purpose, the electrode structure of the one (right) output In comparison with the other output transducer, the converter is mirrored so that two signals which are 180 degrees different or phase-shifted are obtained at the two output terminals. For the additional signal, therefore, an additional outer housing contact is required. In a modification of the interconnection shown in Figure 4, the two output terminals are guided separately from each other through the base plate and connected to separate outer housing contacts in a symmetrically operated at the output filter. Accordingly, the number of minimum required outer housing contacts increases to five.

FIG. 6 shows capacitors connected in parallel with the parallel resonators with which the edge steepness of the filter can be improved, in particular the left flank of the passband. The capacitances are advantageously realized on the substrate surface in the form of pads or as interdigital structures. FIG. 6a shows such a capacitance in the schematic equivalent circuit diagram. FIG. 6b shows an embodiment as adjacent metallization surfaces, between which the capacitor CA can form. FIG. 6c shows a capacitance designed as an interdigital structure, which has a shorter finger period than the converter of the parallel resonator. Figure 6d also shows an interdigital structure rotated 90 degrees in orientation on the substrate from the orientation of the parallel resonator. In addition, the finger period may be even smaller than that of the interdigital transducer. With capacitances CA connected in parallel with series resonators, the steepness of the right flank of the passband can also be improved. FIG. 7 shows a transfer function S21 obtained with a filter according to the invention (see curve a) in comparison with the transfer function of a filter according to the prior art (curve b), which comprises two series-connected 3-transducer DMS structures and additionally one parallel resonator each at input and output contains. It can be seen that the proposed filter is significantly improved in terms of both edge steepness and backbone suppression.

FIG. 8 again shows, with reference to two exemplary transfer curves S21, the effect of the separated masses on the filter behavior. The transmission curves S21 of two filters are compared, namely a filter designed as shown in FIG. 4 (see curve a) with a similar filter in which the ground surfaces C2 and C4 of the middle metallization plane MM are directly connected to one another (see curve b). , Clearly, the significant effect on edge steepness (left flank) and backbone suppression is evident.

FIG. 9 also shows the advantage of separate grounding by comparing the transmission curve of a filter according to the invention (see curve a) with the transmission curve of a filter in which the ground connections corresponding to points C4 and C5 in the middle metallization level MM the first two parallel resonators are interconnected (see curve b). Again, the improvement in selection and, in particular, improved suppression of backbone, are evident.

FIG. 10 shows an effect which results from the electrical connection of the cover as proposed is effected. Compared here is the transmission curve a of a connected as in Figure 2 lid, which is connected via an inner housing contact L3 and a via to the ground plane C2 and via the inner housing contacts Ll and L2 and one through-connection to the ground C4. This filter is compared with a symmetrically connected cover, in which an equal number of plated-through holes is guided to the ground surfaces C2 and C4. (Curve b). It can be seen that the asymmetrical cover connection also achieves a positive effect with regard to selection and, in particular, counterband suppression.

FIG. 11 shows a resonator which is divided into two series-connected partial resonators TRI and TR2. The finger arrangement in FIG. IIb is such that the phase of the acoustic wave coincides in the two partial resonators. In contrast, in FIG. 11a, the phase of the acoustic wave in the two partial resonators is offset by 180 °. A resonator divided into sub-resonators can be used as a series resonator and as a parallel resonator and improves the power compatibility of the corresponding resonators.

The proposed filter is not limited to the exemplary embodiments and can be varied depending on the number of available outer housing contacts within the scope of the invention. The housing may be constructed from only one or from further dielectric layers and further metallization levels. Also with regard to the materials deviations from the proposed ones are possible. The first sub-filter may also be arranged on a separate second substrate or constructed of other than SAW resonators, for example, resonators working with bulk acoustic waves BAW. LIST OF REFERENCE NUMBERS

SU substrate

TFl first subfilter

Sl, S2, S3 series resonator

Pl, P2, P3 parallel resonator

TF2 second subfilter

GKi inner housing contact

GKa outer housing contact

GP base plate

DLl, DL2 dielectric layer

TRI, TR2 partial resonator

D lid

Gl to G5 inner body contacts for ground

Ll, L2, L3 cover contact connection surfaces

I inner housing contacts for input

O inner housing contacts for output

Cl to C5 inner metallization surfaces

MM Medium metallization level

CA capacity

MA ground connection

El to E4 outer housing contacts

VI through-hole

BU Bump

IN entrance

OUT output

Claims

claims

1 . HF filter

with at least one substrate (SU),

- With a first sub-filter arranged thereon

(TF1) comprising a series resonator (S) and two parallel resonators (P) each arranged in a parallel branch,

with a second partial filter (TF2) designed as a DMS filter,

- With a housing comprising a base plate (GP) with at least one dielectric or non-conductive layer (DL), a number of inner housing contacts (I, G, O) on the base plate, which are connected to pads on the substrate, and on the other hand a smaller number of outer housing contacts (GKa) on the underside of the base plate, which are connected to the inner housing contacts via leads routed within the housing,

- With at least two separately guided in or on the base plate lines for ground connections of the first parallel resonator and the second sub-filter, which are connected to at least two different outer housing contacts.

2. Filter according to claim 1, in which the baseplate (GP) has at least two dielectric layers (DL1, DL2) and a metallization plane arranged therebetween, which is structured via interconnections (VI) with the inner (GKi) and outer housing contacts ( GKa) is connected.

3. Filter according to claim 1 or 2, wherein the ground terminal of the first parallel resonator (Pl) via vias directly without further interconnection with the first outer housing contact (E4) is connected.

4. Filter according to one of claims 1 to 3, wherein the ground terminals of the first and second parallel resonator (Pl, P2) are guided separately from each other and both with the first outer housing contact (E4) are connected.

5. Filter according to one of claims 1 to 4, wherein a second series resonator (S2) and in a third parallel branch, a third parallel resonator (P3) are provided, wherein the ground terminal of the third parallel resonator is connected to the second outer housing contact.

6. Filter according to claim 4, wherein in addition a third series resonator (S3) between the second series resonator (S2) and the DMS filter (DMS) is provided.

7. Filter according to one of claims 1 to 6, wherein the DMS filter (DMS) comprises a track with five transducers or two parallel tracks, each with three transducers.

8. Filter according to one of claims 1 to 7, wherein at least the first or the first and the second series resonator (S) are cascaded, so that it in two in Series switched partial resonators (TR1, TR2) is divided.

9. Filter according to one of claims 1 to 8, wherein at least the first or the first and the second parallel resonator (P) are cascaded, so that it is divided into two series-connected partial resonators (TR1, TR2).

10. Filter according to one of claims 1 to 9, wherein the first sub-filter (TFL) has an asymmetrical input and the second sub-filter (TF2) has an asymmetrical output, wherein the housing has four or five outer housing contacts (GKa).

11. Filter according to one of claims 1 to 9, wherein the first sub-filter (TFL) in a single-ended input and the second sub-filter (TF2) has a balanced output, wherein the housing has five or six outer housing contacts (GKa).

12. Filter according to one of claims 1 to 11, wherein the ground terminals on the substrate (SU) are connected to each other with high resistance.

13. The filter of claim 12, wherein the ground terminals are connected together by a meandering structure having a resistance of more than 1 kΩ.

14. Filter according to one of claims 1 to 10, wherein in the second sub-filter (TF2) for each two adjacent terminal electrode fingers of different transducers applies that either both are connected to the signal line or both connected to a ground terminal.

15. Filter according to one of claims 1 to 11, wherein the substrate (SU) in the housing between the base plate (GP) and a lid (D) is arranged, wherein the lid comprises at least one electrically conductive layer, wherein the lid is electrically connected to the interconnection in the base plate and thereby connects the ground terminals of the filter together.

16. The filter of claim 15, wherein the lid (D) is connected to the unbalanced connection.

17. Filter according to claim 16, in which the cover (D) is connected to the outer housing contacts (GKa) via plated-through holes (VI), wherein the connection to the input side ground terminal comprises more vias connected in parallel than the connection to the output side ground terminal.

18. Filter according to one of claims 1 to 17, wherein in the base plate (GP) has two separate inner

Ground planes (C2, C4) are provided, which with several

Ground terminals of the first and second sub-filters (TFl, TF2) are connected.

19. Filter according to claim 18, in which one of the inner ground surfaces (C2, C4) is connected to an outer housing contact (GKa) via a plurality of parallel plated-through holes (VI).

20. Filter according to one of claims 1 to 19, wherein between the second sub-filter (TF2) and the output (OUT), a third sub-filter is connected, which consists of at least one parallel resonator and at least one series resonator.

21. Filter according to one of claims 1 to 20, in which parallel to the parallel resonators (P) capacitances (CA) are connected.

22. Filter according to claim 21, wherein the capacitances (CA) are realized in the form of metallizations on the substrate SU).

23. Filter according to claim 16 or 17, wherein the capacitances (CA) are formed as an interdigital structure.

24. The filter of claim 18, wherein the interdigital structures of the capacitances (CA) are rotated with respect to the interdigital structures of the parallel resonators (P).

25. Filter according to one of claims 1 to 24, wherein the input (IN) and output (OUT) are reversed.